We've come very far in terms of understanding the body, but we have a way to go to truly understand how the brain works. Here's a quote from the prescriber information for Vyvanse (emphasis is mine):

The mode of therapeutic action in Attention Deficit Hyperactivity Disorder (ADHD) is not known. Amphetamines are thought to block the reuptake of norepinephrine and dopamine into the presynaptic neuron and increase the release of these monoamines into the extraneuronal space.

By testing in petri dishes, animals, and humans, we are able to establish the efficacy of drugs even if we don't completely understand the mechanism of action. However, there are side effects to every medication, and some patient populations that can't take the medications at all. Whenever there are alternative ways to heal people, it's a good thing. As science and technology advances, let's hope that we are able to treat people with no side effects at all!